Method of refining zinc



Oct. 28, 1930. F. R. KEMMER METHOD OF REFINING' ZINC Filed May 2. 1928 Frank Kemmer INVENTOR W ATTORNEY Patented Oct. 28, 1930 UNITED STATES.

PATENT OFFICE FRANK R. KEMMER, 0F LARGHMONT, NEW YORK, ASSIGNOR TO AMERICAN GYANAMID COMPANY, OF NEW YORK, N. Y., A CORPORATION OF MAINE METHOD OF REFINING ZINC Application filed May 2,

This invention relates to the production of zinc, more particularly to the treatment of,

raw or crude zinc for the purpose of making the same marketable.

In the recovery of zinc by electrothermic methods and more especially when electrothermically smelting complex ores, concentrates and other metallurgical products and residues containing in addition to zinc, such valuable metals as lead, copper, silver and gold, it has been found that when such complex ores are smelted in an electric are or combination arc and resistance type of smelting furnace, in addition to the zinc and lead which are practically, entirely reduced to metal in the vapor stage, there are likely to be found co-existing with such vapors, especially when great care is not exercised in the smelting operation, vapors of other metals, alloys or compounds of iron, copper, cadmium, silver, etc., depending. on the presence, state of combination and pro ortion of such other elements in the zinc earing charge to be smelted. In such case the product resulting from the direct condensation of such vapor to liquid metal or from the .con- 7 version of zinc powder to liquid metal in case the vapor is first condensed to zinc powder,

7 as has been the heretofore customary commercial vpractice is known as crude or raw zinc and this is an impure product for which there is no regular market.

In order to make the c'rude'zinc merchantable itv must be treated further and this treatment has consisted of transferring such raw or crude zinc into a box type of furnace in which the crude zinc is maintainedin a molten condition by the use of any of the well-known heating agents, such as electric heat.

As practiced heretofore by one known process the ,"crude zinc has been permitted to liquate at a temperature just above the smelting point of zinc, namely, 419 C. andpreferably not exceeding 435 C. At this tem- 1928. Serial No. 274,401.

,perature the crude zinc separated into three distinct products, namely, raw lead which collected on the bottom of the furnace in a liquid condition, hard zinc which separated out above the raw lead as a crystalline or mushy material and which contained in the neighborhood of one and one-half to two per cent of iron and finally above this wasthe third product, namely, spelter. Operation of this liquating furnace at a temperature very near to the melting point of zinc was neces sary in order that the top layer of zinc might not dissolve a quantity of iron above that which would permit its being classified as prime western or G. O. B. spelter. However, when operating at this temperature, the spelter as a rule had to be ladled from the furnace and the hard zinc removed by hand more or less continuously to avoid clogging of thefurnace. This was a laboriousopera"- tion which interfered with the continuous operation of the furnace and also resulted at times in some of the casts of spelter being off grade. The hard zinc containing approximately one and one-half to twoper cent iron had been refined heretofore in ,an electric arc'type of furnace-in which the zinc was volatized and condensed as aproduct considerably better in quality than prime western or G. O. B.' spelter but not quite of as good quality as grade A zinc of 99.9 per cent purity, The iron remained in the refining furnace with some zinc, lead, copper, silver and gold as a complex roduct, more or lessdifficult to handle an prepare for shipment and with the valuable metals such as copper, lead, silver and gold so diluted by the iron as to considerably reduce their commercial value.

The crude spelter as produced by electroethermic smelting metho s as a rule contains an appreciable amount of silver and at tunes may contain an appreciable amount of copper and one of the drawbacks of the describedmethod of operationwas that these valuable metals have had to be marketed in this form at the same price as the spelter itself. In some cases, the presence of copper may be objected to as being detrimental for the particular use to which the spelter was to be P I have discovered that it is possible to effect important improvements in the methods as heretofore practiced and my invention relates to a method of treating raw or crude zinc whereby the quantity of hard zinc produced will be materially reduced and whereby the copper, silver and any gold formerly disposed of in the spelter will be recovered in a more valuable form and whereby the grade of spelter will be so improvedas to command a premium above the price of prime western or G. O. B. spelter.

According to my invention I place raw or crude Zinc in any suitable type of furnace for maintaining the crude zinc in a molten condition. I depart however, from the usual practiceof maitaining the furnace contents at a temperature just above the melting point of pure zinc (419 C.) for the removal of spelter of low iron content of .0570 or less. In practicing my invention, the furnace contents of crude zinc may be maintained substantially above the melting point of zinc, say at 450 C., or higher, the raw or crude zinc is permitted to separate into three products as heretofore, but under the higher temperature used I find that the percentage of iron in the hard zinc is increased and thereby the quantity of hard zinc made is substantially reduced and likewise the amount of refining to be performed in the arc furnace is correspondingly reduced. I also depart from previous practice in not attempting to make mercha-ntable spelter but by transferring the top layer of zinc to an electric distilling or refining furnace wherein heat'is generated by means of resistors of any of the well known types and construction I am enabled by careful temperature control to obtain a zinc of high degree of. purity and which will command a premium above the prime western or G. O. B.

brands.

Indeed, I find that if the zinc bearing material to be smelted has been practically freed of cadmium as in the final stage of roasting as, for example, by finishing the roasting of the ore on a Dwight-Lloyd machine, I am enabled by careful temperature control to obtain from the resistor refining furnace a product which will command the full going premium of grade A zinc The residue left in the resistor fprnace will contain in merchantable form any'c opper, lead, silver, gold and other valuable and precious metals which have heretofore been retained in the speltcr and which have heretofore commanded a price considerably below their value when sold as a residue or cake resulting from the refining operation.

As a specific example of the substantial reduction in the quantity of hard Zinc produced, I will assume 1000 pounds of raw zinc containing ten per cent (10%) lead and one half per cent (0.5%) iron. In the following tabulation column I shows the percentage of iron in the hard zinc.- column 2 shows the corresponding quantities in pounds of hard zinc, and column 3 the corresponding pounds of spelter.

I II III 2.0 250 650 3.0 167 733 4.0 125 775 5.0 100 800 It is evident that for the best metallurgical results I- will remove from the contents of the liquating furnace the top layer at one stage of the operation when the temperature is relatively low as compared with the temperatures at which the hard zinc is removed and, as actually practiced on a large commercial scale, sufli cient liquating furnaces are in use so that it is possible to carry on all operations more or less continuously by operating in such a manner that one can be transferring the top layer of zinc from the liquat-ing furnace maintained at one temperature to the resistor refining furnace or furnaces at the same time one is transferring from a different liquating furnace which is maintained at a higher tempera ture the contents of hard zinc to the are type of zinc refining furnace.

In the accompanying drawing constituting a part hereof and in which like character references indicate like parts;

Figure 1 is a vertical, longitudinal. crosssectional view of a liquating furnace adapted for the practice of the present invention. and

Figure 2 is a vertical transverse cross-sectionalview of said furnace taken along line 22 of Figure 1.

The raw zine obtained either by the electrothermic process above described or by any other method, and which may contain in addition to zinc large quantities of lead and smaller quantities of iron, copper, cadmium, gold and silver is charged into a liquating furnace 1, which is preferably in the form of a box made of or lined with refractory material, having an opening 2 at one end thereof for the introduction of liquid raw zinc into the same for refining purposes and having an outlet 3 at the opposite end of the furnace for the removal of refined molten zinc, commonly called spelter. In the space 4 above the level of liquid in the furnace are carbon electrodes 5, 6 and 7 placed horizontally and so connected on the'exterior of the furnace as to allow any one or all of the electrodes to be operated in any relation desired, in order to obtain and maintain mercial' spelter.

furnace of the products resulting from the liquating operation.

Generally the operation of my inventio is accomplished as follows: Raw zinc is charged into the furnace in the liquid form at point 2, flowing into the furnace and filling the same to the level 11. which is higher than point 12 thus forming a seal. Electrodes 5 and 6 are energized producing heat which is radiated on to the raw Zinc, causing the constituents thereof to separate out into two or three layers, depending upon whether lead is absent or present in substantial amounts. If it is present a layer of crude lead is formed in the bottom 13 of the furnace and may be tapped off at will through tap hole 8. The temperature of the liquating portion of the furnace is maintained at the desired degree above 450 C. and ordinarily I may operate'between 500 C. and 775 C., say at 700 C. The high temperature used causes the formation of a layer ll of hard Zinc containing generally more than :2 per cent of iron and generally over 5 per cent thereof. In some cases I may so operate the furnace as to obtain a layer of hard zinc containing even 10 or 11 per cent of iron with a correspondingly lesser volume thereof. The layer of hard zinc ll may be removed from the furnace either through a tap hole 9 or by raking. the same out through opening 2. and if it contains a high percentage of iron it may be thrown back directly into the smelting furnace whereby the precious metal contained therein is saved.

The layer 15 of zinc travels gradually to the outlet 3 of the furnace. but because of the high temperature at the liquating end of the furnace caused by the electrodes 5 and 6 it may contain an amount of iron too high to allow the same to be sold as com- I, therefore allow the molten zinc to cool at the discharge end of the furnace to a point justabove the melting point thereof, whereby the solubility of the Zinc for iron is gradually reduced and the iron deposits therefrom on the portion 10 of the fioor of the furnace. from which itmay be raked into the body ll of hard zinc. The purifier spelter is then removed from discharge opening 3 and may be sold or refined. This spelter contains the major portion of the copper. silver and gold originally present in the raw zinc and by a simple distillation in a suitable furnace the zinc may be volatilized and condensed, leaving a residue containing the copper. silver and gold. together with small amounts of other metals. This residue may be sold at a high price commensurate with the value of the metals therein.

My invention results in a considerable saving in the production of purified or refined zinc from saw zinc containing varying per- 'centages of other metals. By operating the liquatlng furnace at a high temperature I an inferior price, so that I prefer to charge' the entire amount of hard zinc into the smelting furnace and allow the precious metals to be again recovered without the expenditure of any material amount of energy. For example, in the prior practice where the raw zinc (assumed lead free) containing say 050 per cent of iron was refined at a low temperature in the liquating furnace, there was produced say 500 pounds of hard zinc containing 2 per cent iron and 1,500 pounds of spelter from a ton of material charged. This hard zinc had to be refined to recover the Zinc and the iron, copper, silver, etc., therein brought a very low price on the market.

By my invention I may take the same raw zinc and liquate it at a high temperature obtaining not over 200 pounds of hard zinc containing substantially all the iron and only a very small amount of the copper and silver. The remaining 1,800 pounds or more of spelter containing a major portion of these precious metals may be recovered in merchantable form by distillation. The small amount of hard zinc may be economically distilled to recover the zinc and the other metals may be economically thrown away,.

but preferably I charge the hard zinc back is not increased materially because of the small amount so charged. and the copper and silver are recovered therefrom in the smelting.

These and other advantages result from my invention, the scope of which is setforth in the claims appended hereto.

Vhat I claim is:

1. A method of treating raw zinc which comprises placing the same in a liquating furnace, raising the temperature thereof to a point materially above the melting point of the zinc, ,thus causing the molten mass to separate into at least two layers, the upper layer being spelter containing the major portion of the precious metals, and the next layer being hard zinc containing only a minor portion of the precious metals, distilling the spelter to volatilize and recover refined zinc, and recovering the precious metals as a residue. 7

2. A method of treating raw zinc which comprises placing the same in a liquating furnace, raising the temperature thereof to a point materially above the melting point of the Zinc. thus causing the molten mass to separate into at least two layers, the upper layer being spelter containing the major portion of the precious metals, and the next layer being hard zinc containing only a minor portion of the precious metals, allowing the spelter to cool to permit the precipitation of iron therefrom and removing the molten spelter form the furnace and distilling the spelter to volatilize and recover refined zinc, recovering the precious metals as a residue.

3. A method of treating raw zinc which comprises placing the same in a liquating furnace, raising the temperature thereof to a point above 450 C. thus causing the molten mass to separate into at least two layers, the

' upper layer being spelter containing the ma or portion of the precious metals, and the next layer being hard zinc containing only a minor portion of the precious metals, distilling the spelter to volatilize and recover refined zinc,'and recovering the precious metals as a residue. 7

4.:-A method of treating raw zinc which comprises placing the same in a liquating furnace, raising the temperature thereof to a 5 point between 500 C. and 775 C. thus causing the molten mass to separate into at least two layers, the upper layer being spelter containing a major port-ion of the precious metals, and the next layer being hard zinc containing only a minor portion of the precious metals, distilling the spelter to volatilize and recover refined zinc, and recovering the precious metals as a residue.

5. method of treating raw zinc which comprises placing the same in a liquating furnace, raising the temperature thereof to a point about 700 6., thus causing the molten mass to separate into at least two layers, the upper layer being spelter containing the mam jor portion of the precious metals, and the next layer being hard zinc containing only a minor portion of the precious metals, distilling the spelter to volatilize and recover refined zinc, and recovering the precious metals as a residue.

6. A method of treating raw zinc which comprises placing the same in a liquating furnace, raising the temperature thereof to a point above 450 (1., thus causing the molten mass to separate into at least two layers, the upper layer being spelter containing the major portion of the precious metals, and the next layer being hard zinc containing only a minor portion of the precious metals, allowing the spelter to cool to permit the precipitation of iron therefrom, removing the molten spelter from the furnace, refining the spelter and recovering the precious metals as a residue.

7. A method of treating raw zinc which comprises placing the same in a liquating furnace, raising the temperature thereof to a point between 500 C., and 775 C., thuscausing the molten mass to separate into at least two layers, the upper layer being spelter containing the major portion of the precious metals, and the next layer being hard zinc containing only a minor portion of the precious metals, allowing the spelter to cool to permit the precipitation of iron therefrom, removing the molten spelter from the furnace refining the spelter and recovering the precious metals as a residue.

8. A method of treating raw zinc which comprises placing the same in a liquating furnace, raising the temperature thereof to a point about 700 C. thus causing the molten mass to separate into at least two layers, the upper layer being spelter containing the major portion of the precious metals, and the next layer being hard zinc containing only a minor portion of the precious metals, allowing the spelter to cool to permit the precipitation of iron therefrom, removing the molten spelter from the furnace, refining the spelter and recovering the precious metals as a residue.

In testimony whereof, I have hereunto subscribed my name this lst day of May, 1928.

FRANK R. KEMMER. 

